Basic structure of a Liquid Crystal Display (LCD) comprises a backlight source and a liquid crystal display panel.
As shown in FIG. 1, a conventional liquid crystal display panel comprises an array substrate 103, a color filter substrate 105 and liquid crystals 104 provided between the array substrate 103 and the color filter substrate 105. Further, a lower polarizing film 102b is provided on the outer side of the array substrate 103, an upper polarizing film 102a is provided on the outer side of the color filter substrate 105, and the polarization directions of the upper polarizing film 102a and the lower polarizing film 102b are perpendicular to each other.
Light emitted from the backlight source 101 is converted into linearly polarized light after passing through the lower polarizing film 102b on the outer side of the array substrate 103. If different electric fields are applied to the liquid crystals 104 at different locations to drive the liquid crystals 104 to rotate in different directions, the polarization direction of the linearly polarized light may be deflected to different extents, and thus the linearly polarized light has different transmittances when passing through the polarizing film 102a on the outer side of the color filter substrate 105, which results in emitted light with different brightness and enables a LCD to present a colour display with different grayscales.
The inventor of the present invention realized that at least the following technical problems exist in the prior art. When an existing LCD displays all black, the polarization directions of the lower polarizing film 102b provided on the outer side of the array substrate 103 and the upper polarizing film 102a provided on the outer side of the color filter substrate 105 need to be exactly perpendicular to each other. However, due to the performance of the upper and lower polarizing films 102a and 102b per se, and rotation performance of the liquid crystals 104 and the like, it is actually difficult to achieve the exactly perpendicular relationship between the polarization directions of the upper and lower polarizing films 102a and 102b. Therefore, light emitted from the backlight source 101 cannot be completely blocked, that is, true black cannot be displayed.